Police investigating the deaths of a Florida man and his family believe he shot his wife and two teenage children, before scattering fireworks and petrol around the mansion they rented from former tennis pro James Blake and turning the gun on himself.

Hillsborough County Sheriff's spokeswoman Donna Lusczynski told a news conference in Tampa, Florida that Darrin Campbell had purchased fireworks, gas cans and gasoline a few days before the family were found dead.

The news comes after a surveillance video emerged apparently showing Campbell purchasing $600 (£360) worth of fireworks just three days before the fire broke out at the home.

The deceased have not yet been formally identified, but the family has not been accounted for and a relative said they were inside the home when it set ablaze on Wednesday morning.

Investigators are now working to determine why Campbell would have shot his wife Kimberly, his 19-year-old son Colin and teenage daughter Megan in the million-dollar, five-bedroom home on one of the most exclusive streets in the area.

Campbell, who has no previous criminal record, shot his family with a 40-calibre SIG Sauer handgun he purchased in July 2013, investigators said.

Police are now combing through the family’s finances and documents retrieved from the home.

Campbell was employed as an executive for a records management firm and the family moved to the area a decade ago and moved to the house to be closer to their children’s school.

Officials have said they are not looking for anyone else in connection with the deaths. The results of the autopsies from all four bodies are still pending.